Beam deflection for temporal encoding in time-of-flight mass spectrometry

Abstract

The pulsed ion sources used in conventional time-of-flight mass spectrometry (TOFMS) generally do not provide adequate resolving power across the mass range required for applications such as gas chromatography combined with mass spectrometry (GC/MS). Theoretical and experimental aspects of beam deflection techniques, which provide time encoding for TOFJMS with continuous ions sources, are explored here. In this approach, ion source conditions do not affect resolving power, allowing for a greater variety of ionization modes to be used. Theoretical predictions for the resolving power attainable with beam deflection, which are satisfactory for GC/MS applications, agree well with experimentally determined values. The combination of GC-beam deflection-TOFMS with time-array detection is evaluated, and the capabilities of this system are compared to those of scanning mass spectrometers.

Orthogonal acceleration time-of-flight mass spectrometry

“…This contributes to a much higher duty cycle than with most conventional TOF systems with``in-line'' gating of continuous ion beams. With most in-line gating, the mass analyzer is receiving ions from the source for a small fraction of the total time of ion production (Yefchak et al, 1990). It is usual for both gating methods to deliver ions to TOF mass analyzers that have substantially less than 100% transmission and detection ef®ciencies.…”

“…The principles of oa-TOFMS embody a marked departure from conventional ways of gating continuous ion beams, as has been stated elsewhere (Yefchak et al, 1990):`T he`orthogonal acceleration' TOFMS instrument recently described by Dawson and Guilhaus (Dawson & Guilhaus, 1989) incorporates beam de¯ection in the broadest sense, but the operating principle of orthogonal acceleration differs suf®ciently from conventional beam modulation techniques to exclude its discussion in this work.'' As a result of the recent rediscovery and the recognition of the potential of oa-TOF, several commercial instruments are now available for a range of ionization methods amongst which electrospray oa-TOF has been the area of greatest activity.…”

Hybrid mass spectrometers for tandem mass spectrometry

“…This was a major focus of the Michigan State work and they developed what was termed a time array detector (TAD). While the TAD is very limited in its capabilities compared with current detection systems for TOF instruments, it was a major development in the early part of the renaissance of TOF mass spectrometry [43][44][45][46]. Recent advances in position sensitive detection technology could make this an interesting configuration to explore for current applications needing high speed data acquisition.…”

An interleaved comb ion deflection gate for m/z selection in time-of-flight mass spectrometry

“…Another use of gate devices for TOF instruments is the temporal encoding of continuous ion beams. 8 The interleaved comb ion deflection gate described here consists of a plane of closely spaced parallel wire segments. Alternate wire segments are connected, creating two distinct wire sets which are electrically isolated from one another.…”

“…In the plate devices the potentials of one or both of the plates are modulated to achieve deflection of unwanted ions and/or selection of the desired portion of the ion beam. [1][2][3]8 This interleaved comb device was first proposed by Loeb to Lusk for use as an electron filter. 9 Lusk's preliminary studies showed that if a high-frequency rf potential was applied between the alternating wire sets, electrons should be eliminated from an ion beam with little effect on the slower ions.…”